Field of the Invention
The invention relates to a method for the manufacture of an insulation moulding, in particular of a refrigerator cabinet, in which the moulding is provided by filling a cavity between an inner and an outer wall of an open-box-shaped mould with a polyurethane reaction mixture and allowing the polyurethane reaction mixture to cure to a polyurethane containing polymer C, the inner and outer wall being arranged in a fixed distance to one another and each wall comprising a bottom face and a plurality of side faces, whereas the polyurethane reaction mixture is fed through an inlet opening positioned in the middle area of the bottom face of the outer wall, wherein before filling the cavity, the mould is turned with the bottom face of the outer wall downwards so that the polyurethane reaction mixture is foaming upwards to fill the cavity. The invention further relates to a moulding prepared by that process and its use for insulating purposes.
Description of Related Art
It is known that in the production of foams from an isocyanate component and an isocyanate-reactive component containing polyol(s) using a physical blowing agent, it has a positive influence on the insulating effect of the foam to be produced if the physical blowing agent is emulsified in the isocyanate-reactive composition in the form of fine droplets. This positive influence on the insulating effect of the foam to be produced is caused by the fact that the droplets of emulsion that are formed act as nucleating agents for the subsequent foaming process. The more droplets that exist and the finer these droplets are, the more cells there are in the subsequent foam and above all the smaller the cells are. This fact has a direct influence on the insulating properties of the foam obtained in this way, since the smaller the foam cells that are formed, the better these properties are. Good insulating properties are reflected in a low thermal conductivity. The difficulty with the manufacture and processing of such emulsions is their stability, however. This stability is defined by the non-separation of polyol formulation and physical blowing agent on simple storage of such an emulsion under normal conditions with no additional external loading over a period of several hours to days, through to loading via temperature influences and increased pressure and influences of shear forces. Only emulsions that offer precisely this stability at least under normal conditions but preferably also under conditions involving temperature change, pressure changes and/or shear forces are thus of relevance in industry. These maturing processes are generally counteracted by means of a dramatic increase in viscosity up to a doubling of the viscosity of the liquid polyol phase. Since however the processing of emulsions is in any case made more difficult by their non-Newtonian behaviour, excessive rises in viscosity are undesirable.
EP 0 905 160 A1 describes stable emulsions containing blowing agent and incorporating polyether alcohols having a functionality greater than 1.5 and a hydroxyl value of 10 to 100 mg KOH/g as reactive emulsion stabilisers (see paragraph [0014]) in the polyol component for producing rigid foams based on isocyanates (see paragraph [0001]). The emulsions contain polyether alcohols, which are produced by the addition of low alkylene oxides, preferably ethylene oxide and/or propylene oxide, to OH- and/or NH-functional starter substances, for example sugar alcohols and aromatic amines (see paragraph [0025]). Polyester alcohols produced from polyfunctional carboxylic acids and polyfunctional alcohols are preferably also added to the polyether alcohols (see paragraph [0026]). The blowing agent is emulsified in the polyol mixture and a stable emulsion is obtained (see paragraph [0021]). The blowing agent can however also be added to the polyol mixture in or just in front of the mixing head. The specific combination of the three polyols A1a, A1b and A1c mentioned in the introduction is however not disclosed in this document. In particular, no polyester polyether polyols are disclosed.
US 2002/0169228 A1 claims a phase-stable polyol mixture comprising a propylene oxide-polyether polyol co-started with sucrose and dipropylene, a polyester polyol and a hydrocarbon having 4 to 6 carbon atoms as blowing agent, which is phase-stable for at least 24 hours (cf. claim 1). A polypropylene oxide-polyether polyol having an OH functionality of between 3.5 and 4.5 started with toluene diamine can additionally also be added to the mixture (see paragraph [0020]). The polyester polyol is started with phthalic anhydride (cf. claim 3) and is preferably STEPANPOL 2352, which is based on phthalic anhydride and diethylene glycol (see paragraph [0022]). Cyclopentane can be used as the blowing agent (see paragraph [0029]), which is either present in the polyol mixture in the form of a microemulsion (see paragraph [0006]), is added to the polyol mixture just in front of the mixing head or is fed to the mixing head as a separate stream (see paragraph [0027]). The polyol mixture is reacted with an organic polyisocyanate to form a polyurethane foam (cf. claim 17). The term “microemulsion” within the meaning of this application implies that the blowing agent is dissolved in the polyol mixture; see paragraph [0006]. This also becomes clear in paragraph [0013], where it is disclosed that the polyol mixture is no longer classed as phase-stable if it has a “cloudy appearance”. The statement that the polyol composition has to remain phase-stable for at least 24 hours (see paragraph [0006]) suggests that the term “microemulsion” is used erroneously in this application. A true microemulsion is in the state of a thermodynamic minimum and is thus stable indefinitely, provided that the composition and temperature do not change. Unlike such microemulsions, emulsions are above all temperature-sensitive but also substance-sensitive. Heating and then subsequently cooling them to the starting temperature generally leads to an irreversible change in the disperse structure, which can cause the emulsion to break. Therefore maintaining the stability of a “true” emulsion as in the present invention is considerably more difficult than in the case of “microemulsions”.
The application US 2002/0169228 A1 refers consistently to the solution of the blowing agent in the polyol mixture. According to this document all factors adversely affecting the solubility of the blowing agent should be avoided, which is why only propylene oxide is used in the production of the polyether polyols (see paragraph [0018]).
WO 00/24813 A1 describes the production of rigid polyurethane foams for the thermal insulation of refrigerators, for example (page 1, lines 3 to 5). The foams consist of organic polyisocyanates, a polyol mixture comprising polyether and/or polyester polyols, a blowing agent and further auxiliary agents and additives (cf. claim 1). The blowing agent consisting of cyclopentane and water is dispersed in the polyol mixture (cf. claim 1). The polyether polyols are produced by addition polymerisation of a polyhydroxyl alcohol with polyethylene oxide and/or propylene oxide (page 4, lines 11 to 15) and preferably have 3 to 6 OH groups (page 5, lines 13 to 15). Glycerol, sorbitol, sucrose and aromatic amines for example can be used as polyhydroxyl alcohols (page 5, lines 1 to 3 and 6 to 7). The polyester polyol can be produced from dicarboxylic anhydrides (e.g. phthalic anhydride) and diols (e.g. diethylene glycol) (page 5, lines 16 to 31) and preferably has two functional groups (page 6, lines 4 to 6). Polyether polyols started on aromatic amines are disclosed in this document in the comparative examples (“polyol K”). In these comparative examples pentane is dissolved and not emulsified in the polyol component (cf. Table 1 on p. 13). The content of polyol K is relatively high, at 40% (comparative example 1) and 50% (comparative example 2) respectively, relative to all polyols present.
Regarding the production methods, mouldings for refrigerator and/or freezer cabinets are typically produced by using moulds of the desired geometry and injecting a PUR/PIR-formulation through an inlet opening typically positioned at the edge between the later back wall and bottom of the cabinet.
A different approach is followed in EP 0 289 764 A2, in which a method as stated above applied, i.e. the polyurethane reaction mixture is injected through approximately the middle point of the later back wall of the refrigerator cabinet, whereas the mould is turned with its back side downwards during the foaming, so that the back wall is essentially horizontal. Although some improvement could be achieved with respect to the foam injection through an inlet opening typically positioned at the edge between the later back wall and bottom of the cabinet, the thermal insulation properties is not always satisfying. In particular the homogeneity of the foam is sometimes not satisfactory.
The objective of the present invention was to provide a method or the manufacture of an insulation moulding, in particular of a refrigerator cabinet, which provides improved thermal insulation properties, whereas these insulation properties should be in particular mostly identical at all positions of the moulding.